Signaling



Sept; 29, 1936. J. 1.. CALLAHAN SIGNALING Filed Jan. 13, 1930 Q I. r INVENTOR J-L.CALLAHAN ATTORNEY w an A w QM .NNQ Q 4 m hm R E m Q w v w Patented Sept. 29, 1936 UNITED STATES SIGNALING John L. Callahan, Brooklyn, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application January 13, 1930, Serial No. 420,316

4 Claims.

This invention relates to a signaling system wherein intelligence is transmitted according to alternating energy, keyed or otherwise acted upon.

According to this invention, alternating energy keyed according to signals to be transmitted is rectified and the rectified component applied to an extremely stable and rapid acting amplifier system controlling a polarized relay, which inturn, controls a utilization circuit such as a radio transmitter. In order to provide an extremely stable and rapid acting amplifier, according to this invention, electron discharge devices forming part of the amplifier are conductively connected to resistance networks carrying unidirectional current. Direct connection of the input electrodes of the devices to the resistance networks is thus made possible; for, with the networks carrying current, high output potentials are precluded from the control or input electrodes of the devices. By the use of resistance interconnection of the amplifiers, it has been found that stability is materially enhanced and that speedier action thereof is obtainable.

The features which are characteristic of this invention are defined with particularity in the appended claims. However, the invention both as to its organization and mode of operation may best be understood by referring to the accompanying drawing in which is shown by Way of illustration and not by way of limitation, a system involving the principles of the present invention.

Referring to the drawing, relatively low frequency energy generated by a suitable generator 2 is keyed or acted upon in any suitable fashion by a keying device 4 which may be of any type, high speed, low speed or automatic, and transmitted over land line 6 to a rectifier or detector 8. To the output circuit of detector 8 there is coupled a low pass filter l0 by-passing energy of frequencies corresponding to that generated by generator 2 but passing energy of key frequencies.

The output appearing in the terminating resistance l2 of band pass filter H1, is applied through a suitable biasing source of potential l4 to an electron discharge device [6 acting as a limiter. Limiter tube I6 is normally biased to carry current but with the presence of detected signal energy in resistance l2, output or anode current therethrough is cut off.

The output circuit of limiter tube I6 is coupled to an amplifying system comprising electron discharge devices !8, 20. The output electrode or plate of limiter tube i6 is coupled or conductively connected purely resistively to the input or control electrode of tube [8 by means of a resistance network 22, 24, 26, 28. In a similar manner the anode or plate of tube I8 is conductively connected with the control electrode or grid of tube 2E9 through another resistance network comprising resistances 30, 32 and 36. In this way tubes I6, IB and 20 are cascade connected to each other through both resistance networks which are connected directly across a source of potential 38.

In the network A, including resistances 22 to 28 inclusive, the resistance values are so chosen that in the absence of output signaling current in resistance l2, tube I8 is biased to cut off. On the other hand resistance network B, including resistances 30 to 36 inclusive, is designed to bias the grid of tube 20 slightly positive so that tube 20 has a unidirectional component normally flowing in its output circuit.

In the output circuit of tube Hi there is connected one coil 40, and in the output circuit of tube 20 there is connected another coil 42 of a polarized relay C having an armature i4. Accordingly, from what has preceded, in the absence of detected keyed energy armature 44 contacts with its lower contact 46, by virtue of the current flowing through coil 42, applying a suitable potential from sources 48 to a utilization circuit such as transmitter 50 for control thereof. Preferably in the absence of rectified keyed energy transmitter 50 is acted upon by the biasing source 48 so that no energy appears in the antenna 52.

With key 4 closed, of course, a reverse state of aifairs is made to exist, tube i8 is caused to draw current and tube 2|] is biased to cut off whereby coil acts to pull armature 44 into contact with the other contact 54 of polarized relay C thereby energizing antenna 52.

Choke coils 56 and condensers 58 are provided as shown for the purpose of preventing the building up of any interfering potentials alternating or otherwise on the grids of amplifier tubes I8, 20, there being a possibility of interfering voltages being present in the common battery source.

To summarize the operation of the system, in the absence of keying current and hence absence of detector output, limiter tube I6 draws current. At that time the steady current flow through the resistance network A is such that amplifier i8 is biased to out off, and the unidirectional flow of current through resistance network B is such that amplifier 20 draws current thereby moving armature 44 of relay C into one controlling position; namely, in contact with contact 46.

With key 4 closed, detected current appearing in resistance l2 biases limiter tube 16 to cut off which, because of the lessened current flow through resistances 24 and 22 of network A, causes the grid of tube I8 to raise in potential to such an extent that tube I8 passes current. With tube 18 passing current, the current passed through resistance 30 of network B causes the potential on the grid of tube 20 to be changed from a positive value to a negative cut ofi value. In this manner coil 40 of polarized relay causes the armature 44 to be moved into its other contacting position whereby antenna 52 is energized. Of course, for reverse signaling, the potentials applied to a transmitter from source 48 may be reversed whereby for closing of key 4, antenna 52 is deenergized.

It is to be noted that the continual unidirectional flow of current through resistance networks A and B causes voltage drops of such value that correct biasing potentials are obtained for the grids of tubes I8, 20. In this manner the unidirectional circulatory currents in the networks preclude the application of high positive potentials from source 38 to the grid of tubes I8, 20.

Furthermore other advantages of the described keying unit comprising the resistively coupled tubes are to be noted. As the tube keying unit converts the signal current or rectified tone into reverse current, the system adds considerably to the working speed of the relay following or associated with it. Moreover, the unit has been found especially adapted for use in receiving systems wherein received signals control the presence of tone on a land line. The tone is taken oil the line, amplifier and rectified, and the rectified energy is passed into a tube keying unit as described. The mechanical relay associated therewith is utilized to control an ink recorder or printer. The latter would replace, of course, transmitter 50.

The invention having thus been described, what is claimed is:

1. A signaling system comprising in combination means for varying an alternating current source according to intelligence to be transmitted, means for rectifying the varied current, an amplifier comprising a source of potential, a plurality of separate resistance networks each connected in parallel with said source, a filter circuit interposed between each of said networks and said source, and a plurality of electron discharge devices cascade connected through said resistance networks, the input electrode and the output electrode of each of said devices being connected to separate networks, means for applying the rectified current to the input of the amplifier, and means for utilizing the output of the amplifier to control a transmitter.

2. In combination, a plurality of electron discharge devices, a source of potential, a plurality of circuits connected in parallel with said source to provide direct current paths over which current from said source may continuously flow, resistances in each of said circuits through which the current flowing in said paths may flow, a circuit connecting an output electrode of one device to a point on a resistance in one of said paths, a circuit connecting the input electrode of another device to a point on a resistance in said last named path, a connection between the control grid of said first named device and a point on a resistance in another of said first named circuits, means to supply rectified alternating energy keyed ac cording to signals to be transmitted as input energy to said devices, a polarized relay actuated by the output energy from said devices and a transmitter controlled by said relay.

3. A thermionic amplifier comprising a plurality of thermionic tubes, means for connecting said tubes in cascade comprising, a source of direct current potential, a plurality of resistance networks connected in parallel with said source of direct current potential to continuously draw therefrom steady direct current, a connection between one of said networks and the output electrode of the first of said thermionic tubes, a connection between said network and the input electrode of the second of said thermionic tubes, said last named connection being made at a point on said resistance network such that when said first named tube is conductive said last named tube is non-conductive, means for applying alternating current to the input electrodes of said first named tube, and a utilization circuit connected between the output electrodes of said last named tube.

4. Keying means comprising a source of keying potentials, a plurality of thermionic tubes connected in cascade, a source of direct current potential, a plurality of resistive networks connected in parallel with said direct current source to continuously draw direct current from said source, circuits for connecting the anode and grid electrodes of adjacent tubes to the same network, the grids of said tubes being maintained at such potentials that adjacent tubes are alternately non-conducting and conducting and vice versa, a connection between the input electrode of the first of said tubes and said source of keying potentials, and a difierential keying circuit connected with the output electrodes of a pair of said tubes.

JOHN L. CALLAHAN. 

